This application is entitled to the benefit of and incorporates by reference essential subject matter disclosed in Japanese Patent Application No.2002-96237 filed Mar. 29, 2002.
1. Field of the Invention
The present invention relates to a locating method, apparatus, system and program for locating the position of a lightning strike from the time difference of the arrival of lightning electromagnetic waves at several receiving stations, and more particularly relates to a lightning strike position locating method, apparatus, system and program in which there is no error caused by topography.
2. Description of the Related Art
Such lightning strike position locating system is called an xe2x80x9carrival time difference system. As disclosed in, for example, xe2x80x9cRakurai Ichi Hyotei Sochi (LPATS-T)xe2x80x94Denryoku Setsubi no Unyoxe2x80x94Hoshu Taisaki Shienxe2x80x94[Lightning Position and Tracking System (LPATS-T)xe2x80x94Support for Operation and Maintenance of Power Equipment]xe2x80x94Toru Shioda, Denki Genba Gijutsu 1998, 7, Special Collection 2, Recent Technical Trends in Lightning Countermeasures, p. 58xe2x80x9d, an arrival time difference system is conceived by applying the principle that the track of points at which the difference between distance from two ground points (equivalent to the difference between arrival time of electromagnetic waves) is constant can be drawn as a hyperbolic curve. As is shown in FIG. 13 of the present application, when there is a lightning strike at a certain ground point, electromagnetic waves generated in the vicinity of the ground surface by this lightning strike (hereafter referred to as xe2x80x9clightning electromagnetic wavesxe2x80x9d) are propagated to the receiving stations R1, R2 and R3 with the respective arrival times T1, T2 and T3. In this case, if time measurement is synchronized among the respective receiving stations so that the instants in time at which the lightning electromagnetic waves arrive at the respective receiving stations can be measured, the arrival time difference among the respective receiving stations can be determined solely from the instants in time at which the lightning electromagnetic waves arrive. Accordingly, on the basis of the above-mentioned principle, hyperbolic curves L12 and L23 corresponding to, arrival time differences, determined by the difference between distance from two arbitrary points, can be determined. Consequently, if the lightning electromagnetic waves are received by receiving stations in at least three different locations, the intersection point X of the hyperbolic curves can be located as the point where the lightning electromagnetic waves are generated, i.e., as the lightning strike position.
FIG. 14 shows the construction of a conventional lightning strike position locating system. As is shown in this figure, a conventional lightning strike position locating system comprises receiving stations R1, R2 and R3 in at least three different locations which receive the lightning electromagnetic waves generated by the lightning strike, and a lightning strike position locating apparatus Hxe2x80x2 which determines the difference between the arrival times of the electromagnetic waves that arrive at the respective receiving stations R1, R2 and R3, uses the horizontal coordinates of the respective receiving station as a reference to calculate a ground point which has a difference in horizontal distance that would result in such arrival time difference, and takes this ground point as the lightning strike position. The lightning strike position locating apparatus Hxe2x80x2 obtains the horizontal coordinates of the respective receiving stations R1, R2 and R3 from a receiving station coordinate memory 3 that stores the horizontal coordinates of the respective receiving stations R1, R2 and R3, and locates the lightning strike position by the above-mentioned principle using these horizontal coordinates as a reference. The results of the location process are displayed by a display device 6, or are stored in memory, printed and sent to a terminal.
Furthermore, in terms of the above-mentioned principle, it is sufficient if there are receiving stations in three different locations; however, it would also be possible to install receiving stations in four or more locations, and to select three appropriate stations for use in the location process. There is also an empirical rule that the position location process becomes more accurate as the positions of the receiving stations that are used are located at a greater distance from the lightning strike position. Accordingly, receiving stations are ordinarily installed at several locations over a broad area. For example, in Japan, the location of lightning strike positions throughout the entire Kanto, Chubu and Niigata regions has been realized by installing receiving stations at a total of six locations including Kashima, Fukushima, Kashiwazaki, Matsumoto and so on.
Furthermore, the horizontal distance between two points used in a conventional lightning strike position locating system is actually a distance that follows the curvature of the earth; for the sake of simplicity, however, this will be described as a distance connecting two points by a straight line in the present specification.
Errors have been confirmed in lightning strike positions located by such a conventional lightning strike position locating system. Using steel towers for which lightning strikes could be confirmed, the present applicant investigated the discrepancies between the actual positions of steel towers receiving lightning strikes and the positions of these steel towers located by means of a lightning strike position locating system in this case. As a result, it was demonstrated that a shift in the located position by a specified distance in a specified direction occurred when a specified combination of receiving stations was used for lightning strikes on steel towers in a specified region.
The present applicant judges that the cause of such discrepancies was topography. Specifically, lightning electromagnetic waves have the property of propagating along the ground surface. If there are depressions and elevations (also called xe2x80x9cundulationsxe2x80x9d) in the ground surface, the propagation path as viewed from the lateral direction is not rectilinear, but includes indentations and projections. Since the time at which lightning electromagnetic waves arrive at a receiving station from the lightning strike position should depend on the creepage distance following depressions and elevations in the ground surface, the difference between arrival times should be evaluated using creepage distances. In conventional techniques, however, the above-mentioned arrival time difference system in which the ground surface is viewed as an ideal horizontal plane that has no depressions or elevations is employed; accordingly, the difference between arrival times is evaluated using horizontal distances. As a result, in the case of the location of lightning strike positions in the above-mentioned Kanto, Chubu and Niigata regions, there is a conspicuous discrepancy in the located positions of lightning strikes occurring in areas located on the other side of mountainous regions as seen from the receiving stations.
Accordingly, it is an object of the present invention to provide a lightning strike position locating method, apparatus, system and program which solve the above-mentioned problems, and which are free of topography-dependent error.
In order to achieve the above-mentioned object, the present invention provides a lightning strike position locating for locating the position of a lightning strike on the basis of a differences in the times at which lightning electromagnetic waves are received by a plurality of receiving stations, wherein the lightning strike position is located so that the distances from the lightning strike position to the receiving stations are creepage distances following depressions and elevations in the ground surface.
The above-mentioned depressions and elevations in the ground surface may be smoothed to a spatial wavelength that is comparable to the wavelength of the lightning electromagnetic waves.
Furthermore, the lightning strike position locating method of the present invention is a lightning strike position locating method for locating the position of a lightning strike by calculating a ground point having a difference in propagation distance that would result in such arrival time difference by using the difference between the times at which electromagnetic waves generated by the lightning strike arrive at receiving stations in at least three different locations, wherein a ground point having a difference in horizontal distance that would result in such arrival time difference is calculated using the horizontal coordinates of the respective receiving stations as a reference, this ground point is taken as the tentative lightning strike position, and, on the basis of this tentative lightning strike position, the position is corrected to a lightning strike position obtained by evaluating the arrival time difference in terms of the creepage distances following depressions and elevations in the ground surface.
The above-mentioned correction may be accomplished by determining the creepage distances from the tentative lightning strike position to the respective receiving stations following depressions and elevations in the ground surface, using the ratios of these creepage distances to the horizontal distances between the tentative lightning strike position and the respective receiving stations to estimate the times at which horizontal electromagnetic waves should arrive at the respective receiving stations from ground points on lines connecting the tentative lightning strike position and the respective receiving stations, and relocating the lightning strike position using the difference between these estimated arrival times.
The above-mentioned creepage distances may be determined by smoothing the depressions and elevations in the ground surface to a spatial wavelength that is comparable to the wavelength of the lightning electromagnetic waves.
The above-mentioned correction may be accomplished by envisioning a group of regions that are spaced at fixed distances in the longitudinal and lateral directions on a map, setting a correction amount for the lightning strike position which takes into consideration the creepage distances from a representative point within the region to the respective receiving stations in a correction amount map for each region beforehand, using this correction amount map to refer to the correction amount in the region in which the tentative lightning strike position is contained, and correcting the lightning strike position by applying this correction amount to the tentative lightning strike position.
Furthermore, the lightning strike position locating apparatus of the present invention is a lightning strike position locating apparatus for locating the position of a lightning strike by calculating a ground point having a difference in propagation distance that would result in such arrival time difference by using the difference between the times at which electromagnetic waves generated by the lightning strike arrive at receiving stations in at least three different locations, this apparatus comprising tentative locating means that use the horizontal coordinates of the respective receiving stations as a reference to calculate a ground point having a difference in horizontal distance that would result in such arrival time difference, and that take this ground point as the tentative lightning strike position, and correction means that correct the tentative lightning strike position to a lightning strike position obtained by evaluating the arrival time difference in terms of the creepage distances following depressions and elevations in the ground surface, on the basis of the above-mentioned tentative lightning strike position.
The above-mentioned correction means may comprise creepage distance calculating means that determine the creepage distances from the tentative lightning strike position to the respective receiving stations following depressions and elevations in the ground surface, arrival time estimating means that use the ratios of these creepage distances to the horizontal distances between the tentative lightning strike position and the respective receiving stations to estimate the times at which horizontal electromagnetic waves should arrive at the respective receiving stations from ground points on lines connecting the tentative lightning strike position and the respective receiving stations, and re-locating means that re-locate the lightning strike position using the difference between these estimated arrival times.
The above-mentioned re-locating means may also act as the above-mentioned tentative locating means.
The above-mentioned creepage distance calculating means may determine creepage lines that express depressions and elevations in the ground surface by smoothing elevation waveforms on lines connecting the tentative lightning strike position and the respective receiving stations, obtained by searching a map data base that provides map information including elevations, to a spatial wavelength comparable to the wavelength of the lightning electromagnetic waves, and may calculate the lengths of these creepage lines as creepage distances.
The above-mentioned creepage distance calculating means may successively average a plurality of elevation data at a specified sampling interval in the horizontal direction provided by said map data base, and thus convert these data into elevation data at a sampling interval that is comparable to the wavelength of the lightning electromagnetic waves.
The above-mentioned correction means may comprise a correction amount map in which a group of regions that are spaced at fixed distances in the longitudinal and lateral directions are envisioned on a map, and a correction amount for the lightning strike position which takes into consideration the creepage distances from a representative point within the region to the respective receiving stations is set for each region beforehand, and map reference means that refer to the correction amount in the region in which the tentative lightning strike position is contained, and that correct the lightning strike position by applying this correction amount to the tentative lightning strike position.
The above-mentioned correction amount map may be a map in which a group of regions are envisioned dividing the longitude and latitude by specified numbers of degrees, and amounts of shift in longitude and latitude that are to be added to the tentative lightning strike position are set for each region.
The above-mentioned correction amount map may be a map in which correction amounts are set to correspond to sets of receiving stations in three arbitrary locations, and the above-mentioned map reference means may refer to correction amounts corresponding to the set of receiving stations in three different locations used in said tentative location means.
Furthermore, the lightning strike position locating system of the present invention is a lightning strike position locating system which comprises receiving stations in at least three different locations that receive lightning electromagnetic waves generated by a lightning strike, and a lightning strike position locating apparatus that locates the lightning strike position by determining the difference between the arrival times of the lightning electromagnetic waves at the respective receiving stations and using the coordinates of the respective receiving stations as a reference to calculate a ground point having a difference in propagation distance that would result in such arrival time difference, wherein the above-mentioned lightning strike position locating apparatus is the lightning strike position locating apparatus according to any of claims 7 through 14.
A data map base may exist that can be referred to by communications from the above-mentioned lightning strike position locating apparatus.
A correction amount map may exist that can be referred to by communications from the above-mentioned lightning strike position locating apparatus.
Furthermore, the lightning strike position locating program of the present invention is a lightning strike position locating program for locating the position of a lightning strike by calculating a ground point having a difference in propagation distance that would result in such arrival time difference by using the difference between the times at which electromagnetic waves generated by the lightning strike arrive at receiving stations located in at least three different locations to, said program causing a computer to execute: an input procedure for inputting a tentative lightning strike position that is obtained by calculating a ground point having a difference in horizontal distance that would result in such arrival time difference, using the horizontal coordinates of the respective receiving stations as a reference; a map data search procedure for searching a map data base that provides map information including elevations; a creepage line extraction procedure for determining creepage lines that express depressions and elevations in the ground surface by editing elevation waveforms on lines that connect the tentative lightning strike position and the respective receiving stations as obtained from said map information and converting these elevation waveforms to a sampling interval that is comparable to the wavelength of the lightning electromagnetic waves; a creepage distance calculating procedure for determining surfaces distances by a distance integration of these creepage lines; an arrival time estimating procedure for estimating times at which horizontal electromagnetic waves should arrive at the respective receiving stations from ground points on lines connecting the tentative lightning strike position and the respective receiving stations by using the ratios of these creepage distances to the horizontal distances between the tentative lightning strike position and the respective receiving stations; and a re-locating procedure for relocating the lightning strike position by using the difference between these estimated arrival times.
Furthermore, the lightning strike position locating program of the present invention is a lightning strike position locating program for locating the position of a lightning strike by calculating a ground point having a difference in propagation distance that would result in such arrival time difference by using the difference between the times at which electromagnetic waves generated by the lightning strike arrive at receiving stations in at least three different locations, said program causing a computer to execute: an input procedure for inputting a tentative lightning strike position obtained by calculating a ground point having a difference in horizontal distance that would result in such arrival time difference, using the horizontal coordinates of the respective receiving stations as a reference; and a correction amount map reference procedure for referring to a correction amount in the region containing the tentative lightning strike position using a correction amount map in which a group of regions that are spaced at fixed distances in the longitudinal and lateral directions are envisioned on the map, and a correction amount for the lightning strike position which takes into consideration the creepage distances from a representative point within the region to the respective receiving stations is set beforehand for each region, and correcting the lightning strike position by applying this correction amount to the tentative lightning strike position.
The above-mentioned input procedure may input the tentative lightning strike position by communications over the internet or the like.